.beta.-amylases are maltogenic exo-amylases which hydrolyse .alpha.-1,4-glycosidic bonds from the non-reducing ends of amylose, amylopectin, or glycogen to produce the .beta.-form of maltose. The .beta.-form of maltose will isomerize spontaneously in aqueous solutions to a mixture of the .alpha.- and .beta.-form.
.beta.-amylases may be used to produce maltose containing syrups of use in the confectionery-, baking-, and brewing industries.
.beta.-amylases have been isolated from various plants and microorganisms (W. M. Fogarty and C. T. Kelly, Progress in Industrial Microbiology, vol. 15, p. 112-115, 1979). The .beta.-amylases known from plants (barley, sweet potato, and soy beans) and from the Bacillus species B. mycoides, B. megaterium, and B. polymyxa are all enzymes whose activity is inhibited by sulphydryl reagents, such as PCMB (parachloromecuribenzoate) thus indicating that the active site involves an SH-group.
Hitherto only one .beta.-amylase has been described which is not inhibited by PCMB, namely a .beta.-amylase produced by Bacillus circulans (U.S. Pat. No. 4,001,136). The B. circulans .beta.-amylase is more thermostable than the above mentioned .beta.-amylases. However, it is rapidly inactivated at and above 65.degree. C.
In a process for the production of maltose wherein starch in an aqueous medium is hydrolyzed by a .beta.-amylase it is, however, advantageous to use a process temperature of about 65.degree.-70.degree. C. to inhibit retrogradation and to avoid microbial infections.
Therefore, the above mentioned Bacillus circulans .beta.-amylase is less than well suited for commercial use at about 65.degree.-70.degree. C. because of too rigid deactivation.
In U.S. Pat. No. 3.804.715 is disclosed a heat resistant .beta.-amylase which is extracted from wheat bran as described in British Pat. No. 1.130.398. The .beta.-amylase is, however, less attractive in a commercial process as compared with an enzyme derived from a bacterial source because the latter can be produced on a large scale at relatively low costs compared to that of a .beta.-amylase of plant origin.
Therefore, there exists a need for an effective microbial maltogenic amylase preparation which is sufficiently thermostable to be employed at 65.degree.-70.degree. C. for extended periods of time to allow hydrolysis of the starch in an economical way.
It is an object of the present invention to furnish a microbial maltogenic amylase which apart from not being inactivated by sulphydryl reagents as PCMB has a high temperature stability in commercially feasible yields.
The present invention is based upon the discovery that high yields of an extracellular maltogenic enzyme (C599 amylase) having such properties can be obtained by cultivation of a transformed B. sutilis strain. The parent strain Bacillus strain NCIB 11837 for the C599 amylase is a poor producer of the maltogenic enzyme.